The present invention relates to the compositions of associating polymer protective coating films which will protect materials, such as agricultural chemicals, for a period of time and then degrade and release the encapsulated contents to the environment. More specifically, this invention relates to the preparation of ionomer compositions containing compatibilized polymers which will be degraded by microorganisms.
This invention provides a new polymeric system capable of degrading when exposed to the environment. The rate of degradation can be controlled such that the degradation in sunlight and air can be made to happen at any time from a few hours to a few months.
Urea is used extensively as a fertilizer for crops. However, a good deal of material is lost prematurely by leaching. It is desirable to have a coating for the urea which would be essentially impermeable to leaching, but would break down under the proper environmental conditions.
Several approaches to the enhancement of the environmental degradability of plastics have been suggested. These include: (1) the incorporation of particulate biodegradable materials, such as starch, as "fillers"; (2) the introduction of photodegradation-sensitizing groups into the molecular structure of a polymer by copolymerization of a common monomer with a second monomer processing such groups; and (3) the incorporation of small amounts of selected additives which accelerate oxidative and/or photo-oxidative degradation.
The enhancement of the rate of environmental deterioration of plastics through the use of oxidation-promoting additives is known in the prior art. For example, the preparation of degradable polyolefin films containing certain organic derivatives of transition metals is described in U.S. Pat. No. 3,454,510.
Various type additives have been employed in plastic film in order to make the plastic film biodegradable. For example, in U.S. Pat. No. 4,224,416 auto-oxidizable amines are employed. In U.S. Pat. No. 3,994,855 a photolyzable metal compound is employed. U.S. Pat. No. 4,495,311 employs an additive system consisting of a metal compound having at least two valence states and a benzoyl derivative of an organic compound.
In order to effectively and economically utilize a coating to protect urea from leaching it is desirable to have a very thin, essentially defect-free coating. To accomplish this with blends of polymers is difficult because of the inherent incompatibility of blends. The current invention combines a rubbery polymer, which has high impermability to urea, with a thermoplastic polymer, which has a high biodegradability. The two are combined in a fashion such that they have excellent compatibility and make good coatings for urea.
The present invention describes a polymer system which is biodegradable in a coating form on urea. The polymer system of the instant invention comprises a compatible mixture of a sulfonated polymer with an amine terminated polycaprolactone. Compatible mixtures of sulfonated elastomeric polymers and amine terminated polycaprolactones are described in U.S. Pat. No. 4,421,898; however, U.S. Pat. No. 4,421,898 failed to teach or recognize the use of these polymer mixtures in their coating form, such as on urea.